PRODUCTION OF GLASS PREFORM FOR OPTICAL FIBER

摘要

PURPOSE:To allow the control of the refractive index distribution of the glass preform for optical fibers with stable and good reproducibility by supplying additive raw materials to the central flow passage of a burner for synthesizing a core and the 2nd flow passage on the outer periphery thereof at the time of producing the glass preform by a vapor phase shaft deposition method using plural pieces of the burners. CONSTITUTION:The burner 21 for synthesizing the core having a multiple tube structure and the burner 22 for synthesizing a clad of a multiple tube structure are disposed. Gaseous glass raw materials are ejected together with double flames of oxydrogen via the burners 21, 22 and are hydrolyzed. The formed granular glass is deposited on a rotating starting materials, by which the glass preform 25 for optical fibers having the core 23 and the clad 24 is produced. The additive raw materials (e.g.; GeCl4) are supplied to the 1st flow passage 21a at the center of an inner flame generating part 26 of the burner 21 for synthesizing the core and the 2nd flow passage 21b on the outer periphery thereof, by which the glass preform 25 for the optical fibers controlled stably in the refractive index distribution is obtd.